ABCA3 functions as a lipid and phospholipid transporter and is critical for the biogenesis of lamellar bodies. Following our discovery of ABCA3 in alveolar type II (AT2) cells, its importance to lung health and disease has been highlighted by an abundance of compelling reports linking mutations in ABCA3 to various lung disorders, including fatal surfactant deficiency in newborns and chronic interstitial lung disease (ILD) in older children and adults. Building upon our prior work characterizing the basic cell biology of ABCA3, this project will use both integrative and reductionist approaches to define mechanisms and pathways underlying the cellular and organotypic consequences for the lung from the expression by AT2 cells of two distinct classes of mutant isoforms of ABCA3 proteins associated with inherited lung disorders in humans. We have identified several ABCA3 mutations that in vitro exhibit either functional (transporter) or trafficking defects with the later inducing ER stress and cytotoxicity. Furthermore, we have developed a novel transgenic knock-in (KI) mouse model expressing the most common clinical variant of ABCA3 (ABCA3E292V) that develops age dependent parenchymal lung remodeling. Our preliminary data demonstrate that this functional ABCA3 mutant disrupts cellular macroautophagy, producing cytotoxicity by lysosome-dependent and ER stress-independent pathways. Our working model proposes that ILD-associated ABCA3 mutations elicits a class-specific, distinct set of altered AT2 cell responses which then drives abnormal lung injury/remodeling. This project contains three thematically interrelated specific aims that address emerging themes critical to lung cell biology: protein quality control, organelle homeostasis, and cytoprotection. Specific Aim 1 will characterize the mechanisms underlying AT2 cell dysfunction from expression of the transport-deficient ABCA3E292V mutant in vivo. Specific Aim 2 will study the vulnerability of the ABCA3E292V lung to exogenous 2nd hits, and determine the role of concomitant ER stress in promoting and enhancing abnormal lung remodeling. Specific Aim 3 will utilize a second novel KI mouse model of ILD we recently developed bearing the most common ILD-associated mutation of the surfactant protein C (SP-C) gene, SP-CI73T, which we have recently shown to also profoundly disrupt cellular quality control including autophagy. Using this novel bi-genic model, we will then assess the consequences of SP-CI73T co-expression in modulating ABCA3E292V mutation associated pathology. Results from the proposed studies utilizing rare gene mutations in AT2 cells as models will not only enhance our knowledge of the molecular mechanisms underlying the pathophysiology of familial ILD, but also more broadly promote a better understanding of the significance of AT2 cell dysfunction-induced aberrant lung remodeling and provide strategies for future development of targeted therapies for sporadic lung fibrosis.